The present invention relates to a mass spectrometer which can measure masses over a broad range and is excellent in sensitivity and resolution and which can be miniaturized.
In recent years, there is an increasing need for analysis of molecules of larger masses in biochemical and other applications, and an ionizing method for ionizing samples by bombardment with high-speed primary ions or neutral particles has attracted interest accordingly. This method can relatively easily produce ions of large molecules having mass-to-charge ratios of the order of 2000 to 5000 that have been unfeasible with conventional electron bombardment ionization or chemical ionization. At present, none but large-sized mass spectrometers can analyze molecular ions of such large masses. Unfortunately, large-sized mass spectrometers are quite expensive and so the fact is that only limited researchers are able to employ these instruments. Accordingly, small-sized or medium-sized mass spectrometers capable of making analysis up to the region of large masses are required, and various attempts have been made as described below.
A scheme has been developed in which an electric field E and a uniform sectorial magnetic field H are used just like a conventional small-sized or medium-sized mass spectrometer as shown in FIG. 1(a), but the deflection angle .phi..sub.m of ions in the magnetic field is made smaller to extend the measurable range of masses as shown in FIG. 1(b). In FIGS. 1(a) and 1(b), indicated by S and D are an ion source and an ion detector, respectively. The reduction in the angle .phi..sub.m lengthens the orbit of the ions thus to spread the ion beam longitudinally. This deteriorates the transmission efficiency of ions and reduces the sensitivity. Another major disadvantage is that the spread of ion beam increases higher-order aberrations, i.e., second-order and third-order aberrations, with a concurrent reduction in the resolution.
The present inventor has already proposed a mass spectrometer that is excellent in sensitivity and resolution, as described in detail in U.S. Pat. No. 4,480,187, corresponding to Japanese published, unexamined patent application No. 19848/1983. As schematically shown in FIG. 2, this proposed system consists of an ion source S, a uniform sectorial magnetic field H, and a torodial electric field E. This system is characterized by the provision of two electrostatic quadrupole lenses Q1 and Q2 between the ion source S and the electric field H to converge the passing beam of ions in a direction perpendicular to the plane of the orbit of the beam and to diverge the beam radially of the beam.